CHICAGO (CBS) — Police at the University of Illinois at Urbana-Champaign were encouraging students to walk in pairs, or take public transit, in the wake of recent attacks on campus.

WBBM Newsradio’s Nancy Harty reports, in the last two weeks, Champaign and university police have seen about a dozen cases of mob action or robbery on the university’s campus.

Police said the incidents usually involve a group of males attacking one or two victims. Sometimes a female is with the attackers, and uses mace or pepper spray on the victims, according to University Police Capt. Roy Acree.

Investigators do not believe the same group is responsible for every attack, which sometimes leave the victim without a phone. Other times, the victim is beaten, but not robbed.

“I don’t think there are any rhyme or reason of why they’re doing it. I think some of it is just for the mere enjoyment of being able to beat somebody up,” Acree said.

The captain said students should not make themselves easy targets.

“Don’t be walking around with your head in your phone. Keep your earbuds out of your ears. Pay attention to what’s going on around you,” he said.

Acree said university and Champaign police have been working together to put more officers on the streets, both in plain clothes and uniforms.